1. Field of the Invention
The invention relates to a cylinder jacket profile, a method of producing a cylinder jacket profile, and to a rotary printing press.
German Patent No. DE 42 07 119 C2 discloses a conventional cylinder jacket profile. An impression cylinder or sheet guiding cylinder includes a surface coating which is polished parallel to the axis of the impression cylinder. The cylinder jacket profile is formed from cylindrical elevations which are disposed perpendicular to the surface of the cylinder jacket. The cylindrical elevations have a cylinder length of 20 to 200 xcexcm, and the raster definition is 400 to 10,000 points/cm2. The impression cylinder has a chromium surface coating into which the cylinder jacket profile is etched. The cylinder jacket profile is formed of individual, statistically uniformly distributed elevations. The high surface energy of chromium of 78 mN/m is disadvantageous due to the associated contamination problems, namely the smearing of the freshly printed surface, as well as the expensive production technique.
Furthermore, it is generally known that the cleanability of impression cylinders may be improved by applying a nonstick coating, for instance a TEFLON or silicon coating, with a typical thickness of some 20 xcexcm. The large alteration of the surface structure of the impression cylinder as a result of the layer and the associated increased degradation of the print result are disadvantageous. Furthermore, the wear resistance of these nonstick layers and their chemical resistance to the cleaning and printing chemicals are low. In addition, this type of coated impression cylinder often cannot sufficiently hold the sheet in the printing process.
Various techniques are generally known for nonstick coatings with a low surface energy. For instance, amorphous, adamantine carbon layers are deposited in thicknesses of 1 to 10 xcexcm using CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) methods. This way, wear-resistant nonstick layers with low surface energy or surface tension (typically 20-40 mN/m) can be realized for refining or finishing surfaces, for instance of tools.
Colloid technology is a new technology for coating surfaces with a nonstick coating in thicknesses of 100 nm to 10 xcexcm.
This technology takes advantage of the complex formation of a polyelectrolyte with fluorine surfactants. The externally exposed surfactant layer, which itself is only up to 1 nm thick, is distinguished by extreme smoothness and extremely low surface tension (11-16 mN/m).
With inorganic-organic hybrid polymers, by incorporating functional groups of, for instance, perfluorinated silane compounds in the silicate frame, it is possible to generate layers with nonstick properties which are not only water-repellent (hydrophobic) but also oil- and grease-repellent (oleophobic) and which therefore have an improved protective effect. The achieved surface characteristics effectuate a reduced adhesion of dirt particles and thus a good cleaning behavior.
In a sol-gel process, it is possible to produce a coating, for instance by immersion or spraying, as an easy-clean layer on the basis of inorganic-organic nanocomposites with a low free surface energy (approx. 19 mN/m) and a high resistance to scratching and rubbing owing to fluorinated organic groups.
It is also known how to realize surfaces having periodic structures with dimensions in the range between 1 xcexcm and 100 nm by photolithography techniques.
Particularly good cleaning characteristics of surfaces can also be realized using a system of plasma-polymer thin layers.
Further, the so-called lotus effect for self-cleaning surfaces is known. In particular, a self-cleaning surface including an artificial surface structure of elevations and depressions is described in European Patent No. EP 0 772 524 B1. The spacing between the elevations is in the range between 5 and 200 xcexcm, and at least the elevations are formed of hydrophobic polymers or durable hydrophobized materials. The elevations cannot be removed by water or water in combination with detergents.
It is accordingly an object of the invention to provide a cylinder jacket profile which overcomes the above-mentioned disadvantages of the heretofore-known profiles of this general type and which ameliorates the presently existing problems when guiding a sheet in a recto/verso printing operation, and which particularly improves the cleaning behavior of a cylinder jacket profile.
With the foregoing and other objects in view there is provided, in accordance with the invention, a cylinder jacket profile configuration for a rotary printing press cylinder, including:
a sheet-guiding cylinder jacket profile having elevations; and
an easy-clean layer as a surface coating for the sheet-guiding cylinder jacket profile, the easy-clean layer having a thickness of less than 5 xcexcm, in particular approximately 1 xcexcm, and a surface energy of less than 50 mN/m.
According to the invention, the cylinder surface is provided with a surface structure. It is of no importance whether the structure is created on the surface of the cylinder itself or on a layer or covering that is applied to the cylinder. In particular, the cylinder can be constructed with a structured surface by spray techniques, jet techniques or molding techniques. In addition, a coating with a thin and low-energy layer which is easy to clean is provided on the surface in such a way that the dimensions of the surface structure remain substantially unaffected.
According to another feature of the invention, the sheet-guiding cylinder jacket profile includes an anti-wear layer, the easy-clean layer is disposed on the anti-wear layer, for example a chromium layer.
It can be advantageously provided that the layer which is constructed for easy cleaning be applied to a structured chromium layer. Because of the small thickness, the layer can be worn off in the contact region in the elevations after only a few revolutions of the impression cylinder, such that the easy-clean layer is interrupted on the elevations. The chromium layer then takes over the generation of high counterpressure, while the ink barely sticks in the depressions of the jacket profile or is easily removed therefrom due to the easy-clean layer.
According to a preferred embodiment, the cylinder jacket profile is constructed with spherical elevations and/or depressions. This makes it possible to realize a good cleanability of the surface, whereby a sufficiently high counterpressure can also be achieved in the print operation. Besides this, a surface so constructed without corners or slopes can be evenly coated with ease. Alternatively, however, it is possible to provide elevations on the surface in the shape of pyramids, cylinders, spheres, truncated cones and/or in an irregularly structured fashion. In accordance with the invention, the various structural shapes may also be combined.
The structured surface according to the invention allows to guide the sheet without slippage or scratching, while experiencing only slight wear. The low-energy coating which is applied to the anti-wear chromium coating serves for picking up optimally little or no ink in the regions in which the sheet has no direct contact with the cylinder jacket profile.
When the easy-clean layer is not sufficiently wear-resistant, it is worn off during use in the regions of contact with the sheet. But this is not problematic, since the low-energy easy-clean layer is preferably intended to exert its effect only between the contact points of the sheet.
With the objects of the invention in view there is also provided, a method for producing an easy-clean layer on a cylinder jacket profile, the method includes the steps of:
providing a cylinder jacket profile having elevations; and
applying an easy-clean layer as a surface coating for the cylinder jacket profile such that the easy-clean layer has a thickness of less than 5 xcexcm and a surface energy of less than 50 mN/m.
According to another mode of the invention, the easy-clean layer is initially applied as a substantially uninterrupted layer and subsequently removed from the elevations, preferably by contacting the easy-clean layer with a printing sheet during a printing operation.
With the objects of the invention in view there is also provided, a printing press, including:
a cylinder having a jacket surface with a cylinder jacket profile having elevations; and
an easy-clean layer provided as a surface coating for the cylinder jacket profile, the easy-clean layer having a thickness of less than 5 xcexcm and a surface energy of less than mN/m.
According to another feature of the invention, the cylinder is a sheet-guiding cylinder such as an impression cylinder or a sheet transfer cylinder used for a recto/verso printing.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a cylinder jacket profile, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.